There have been several stories recently about genetically modified mosquitoes, bred for the purpose of fighting diseases like malaria and dengue fever. These are exciting, sophisticated techniques, but in a new piece for Slate, I argue that they’re being let down by the fact that we still don’t know a lot about basic mosquito biology, like thier mating behaviour. Ecology may not be as sexy as tinkering with genes, but history teaches us that it’s vital if these approaches are to work.

But all of these recent attempts to turn mosquitoes into malaria- and dengue-killing machines have something in common: The modified mosquitoes need to have lots of sex to spread their altered genes through the wild population. They must live long enough to become sexually active, and they have to compete successfully for mates with their wild peers. And that is a problem, because we still know surprisingly little about the behavior and ecology of mosquitoes, especially the males. How far do they travel? What separates the Casanovas from the sexual failures. What affects their odds of survival in the wild? How should you breed the growing mosquitoes to make them sexier? Big question marks hang over these seemingly straightforward questions.

Heather Ferguson from the University of Glasgow studies mosquito ecology. She views the knowledge gap in this field as a significant obstacle that stands in the way of the GM-mosquito initiatives. History tells us how dismally such initiatives can fare if they are not constructed on solid ecological foundations. In the 1970s and 1980s, several groups tried to control the mosquito population by releasing sterile males that would engage females in fruitless sex. The vast majority of the experiments failed.

Their poor performance is often blamed on the fact that the males were sterilized with damaging doses of radiation. But they had many other disadvantages. Lab-bred mosquitoes are frequently reared in large, dense groups, which produces smaller, less competitive individuals. The artificial lights of a lab could also entrain their body clocks to the wrong daily rhythms, driving them to search for mates at the wrong time of the day. And in several cases, the modified males ignored the wild mosquitoes and preferred to mate with their lab-reared kin instead. These problems went unnoticed in lab tests, where the modified mosquitoes were compared with unaltered ones that had been raised in the same conditions. They seemed to be perfectly competitive, but they proved to be feeble challengers to their wild peers.

Comments (2)

I don’t disagree with the specifics of your argument but I do disagree with the overall conclusion that “we aren’t ready to use genetically modified mosquitoes to tackle malaria and dengue”.

I think this issue needs to be seen in context. Which is:

– the main way of killing mosquitoes and other insect pests at the moment is to use pesticides, which can cause a lot of collateral damage to other organisms, including us. The GM approach is far preferable, so if it works, we should welcome it with open arms

– insects rapidly develop resistance to all pesticides. So there is a double standard here. Why aren’t you writing articles about how we aren’t ready to use pesticides to tackle malaria and dengue, until we understand far more about how we can stop resistance to pesticides evolving?

– if resistance does develop to any one kind of GM mosquitoes – and it’s a big if – it is not the end of the world. The insects can be tweaked to overcome the resistance, or an entirely new genetic strain can be used. The GM approach is far, far more flexible than zapping insects with radiations or sterilising chemicals

– you acknowledge the research you call for will cost a lot of money. Who’s going to pay for this? We need to companies like Oxitec to start making money and lots of it, to give people the confidence invest in this kind of research. Yes, it would be wonderful to do it beforehand, but it is not realistic commercially

Hi Michael. Great comment. I want to clarify that my position is not that we’re not ready to use these techniques, nor that we shouldn’t. It’s that that we need more basic ecological data to make sure that these approaches are most effective. I realise that the hed and URL might suggest otherwise, but as you know, I have no control over those.